1997 5.7 Gi not sucking water until after revved

[nathanj988]

I have temporarily added a clear length of hose on the output of the raw water pump to allow me to see if water is flowing and if there are any bubbles.

My boat won't pull water (or prime) until I rev it up for 2 or 3 seconds. After revving the engine the water is flowing with no bubbles and I can idle for an extended time. If I don't rev the engine the exhaust elbows get hot because of there is no water flow.

I replaced the impellor last fall, however I will probably throw a new one in it soon just to rule that out.

Like I wrote above, I don't have any bubbles, so I shouldn't have any air leaks in the drive unit. The water pump is also not introducing air bubbles so that should be nicely sealed up.

What do I look for?
Thanks,
Nathan

 

[Outsider]

Did you have this problem before you replaced the impeller? :faint2:

 

[nathanj988]

I have only had the boat out one time, but I think so.

It had a number of things wrong that I have been dealing with, but it never liked running a the correct temperature. I am testing it with the drive dipped in a large metal trough or bucket instead of on a hose with muffs. I want the pump to pull the water like it will in the lake instead of the hose pushing the water into the pump with pressure. The tank the drive is dipped in does not have the drive as submerged as the lake will, but it does have all the water intake holes covered with several inches of water.

 

[QC]

Remember, a little deeper and she'll have more head pressure at the water pump. Also, be careful evaluating temp in a bucket. Unless you run a hose constantly in the bucket, then you are recirculating hot water and it will get progressively hotter. The fact that you have no bubbles is positive, but it doesn't mean the impeller is perfect. Where would the air come from if the impeller had a blade missing?

 

[nathanj988]

It is possible that having the drive deeper in the water will make a difference, that is why I mentioned that little bit.

When I first placed the drive in the large metal trough, which is probably 50 gallon or larger, I had to slightly rev the engine (2K RPM) to get the water to start flowing. The next morning the drive was able to prime itself in no time at idle. I later ran the engine without the hose in the bucket and the water level got just below the water intake holes so it lost its vacuum. After I refilled the trough, it needed to be revved to reprime the pump.

It seems that as long as it has been "primed" and there isn't air in the system, it keeps it.

My fear is that without the clear hose, the only way to know if water is flowing is to touch the exhaust risers. That isn't something you are supposed to have to do. The engine temperature doesn't rise fast enough to indicate a problem when the engine is first started, even without the water flowing.

 

[bruceb58]

Having the drive in the bucket, I am surprised it will even prime at all. When its in the water,the pump is at about the level of the water so it is a completely different scenario.

 

[nathanj988]

That is good to hear. I plan on taking it out for a test tomorrow. I had a problem last time but I later found that one of the screws was loose from when I replaced the impellor, it was probably sucking air.